/**
 * Created by LMN on 2016/9/18.
 * Save data from a object to another, without some data whose keys are "except".
 * @param target, the object need to return.
 * @param source, data object.
 * @param except, list of the keys of data which are needed.
 * @return target.
 */
module.exports = function( target, source, except){
    var _except = {};
    if(except){
        for(var i= 0,l=except.length;i<l;i++){
            _except[except[i]] = true;
        }
    }
    for(var key in source){
        if(_except[key]) continue;
        target[key] = source[key];
    }
    return target;
};